Conventional devices for testing the shear strength of soil and/or rock in boreholes, such as that described in U.S. Pat. No. 4,427,871, are inadequate for use in heavily overconsolidated soils in which the vertical pressure is less than it was at some earlier time, such as glacial clays and tills. Generally, such devices are inserted into a borehole and a force normal to the longitudinal axis of the borehole is applied to the material being tested by a shear plate engaging such material, and then an axial force is exerted on the device until the material shears. The test zone is destroyed upon shear of the material, thus requiring the device to be repositioned into a fresh testing zone each time the axial force is applied. This procedure is time consuming and cumbersome, particularly when the material being tested is at a great depth from the land or water surface such as in off-shore drilling investigations.
Therefore a primary objective of the present invention is the provision of a soil and rock testing device having a plurality of independently acting shear heads for testing material surrounding a borehole without need for repositioning the device after the material shears adjacent one of said shear heads.
A further objective of the present invention is the provision of an in situ soil and rock testing device which can be used to test the material at various depths along a borehole.
A further objective of the present invention is the provision of a soil and rock testing device that can be used in determining the shear strength characteristics of the material being tested.
A further objective of the present invention is the provision of a soil and rock testing device which can be anchored anywhere along the length of a borehole.
A further objective of the present invention is the provision of a soil and rock testing device which is durable in use, and provides for easier and more rapid testing.